Google specialist for linking 2 web properties to Analytics, Search Console & YT

I need some help with linking Google services to my website and improving the SEO for my website by fixing any errors Google Search Console.

My main website is built and hosted on Squarespace, https://discoverdoublebass.com but I have the digital products (courses) hosted on a subdomain of my main website using Teachable https://courses.discoverdoublebass.com. I recently moved to this set up from using two different domains to host my main site and products and am now having issues with Google services.

1. YOUTUBE CARDS & END SCREEN CREDITS NOT LINKING TO ASSOCIATED WEBSITE:
Currently I'm struggling to link up YouTube Associated website to my website in order to link to the products (on a subdomain) from my Youtube videos. I can link to the main site using cards and end screen credits, but not the subdomain which hosts the products.
I also have numerous old links in cards (which are being redirected to the new site) and end screen credits which are not pulling preview images which they used to. I've struggled to add new cards unless they are to the home pages of my website. This happened after I moved the products from the top level domain to a subdomain eg, courses.mywebsite... etc..

2. SEARCH CONSOLE ERRORS:
Whilst investigating this I found errors and recommendations in Google Search Console.
I would like someone to fix these issues in order to improve the seo for the site. Plus making sure all relevant Google services such as Analytics are correct and linked up in the best possible way. Currently the Analytics are set up for separately for the main domain and subdomain. I'm not sure if this is the best way to do it and it makes it hard to judge the total numbers of traffic etc.

I am looking for an experienced Google specialist who is able to make sure the website and subdomain are linked up to Google in the best possible way for SEO and to allow links to my websites via YouTube cards/end screens. I also want all errors in Search console fixing.

I welcome proposals for the work via PeoplePerHour, not via email.